1. Field of the Invention
The present invention is related generally to integrated circuits, and more specifically to a contact between different layers of polycrystalline silicon interconnect.
2. Description of the Prior Art
In semiconductor circuits, it is known that ohmic contacts are desirable between interconnect layers. An ohmic contact is one in which no P-N junction is formed.
When polycrystalline silicon interconnect lines having different conductivity types make contact, a P-N junction is formed. A similar junction can be formed when polycrystalline silicon having the same conductivity type, but very different doping levels (such as Nxe2x88x92xe2x88x92 to N+) make contact. For various reasons, it is often desirable to have interconnect having different conductivity types make contact, and it would be desirable to provide an ohmic contact for such structures.
It is therefore an object of the present invention to provide an ohmic contact between polycrystalline silicon interconnect layers having different conductivity types.
It is another object of the present invention to provide such a contact which is easily formed with a process compatible with existing process technologies.
It is a further object of the present invention to provide such a contact which is suitable for use in an SRAM structure to provide a load.
Therefore, according to the present invention, a contact structure provides electrical contact between two polycrystalline silicon interconnect layers. The lower layer has a silicide layer on its upper surface. The upper polycrystalline silicon layer can be doped with a different conductivity type, and makes the ohmic contact with the silicided region of the lower polycrystalline silicon layer.